1. Field of the Invention
The present invention relates to an on-vehicle image pick-up apparatus for picking up a dead angle area on left and right sides on the forward or backward side of a vehicle and a method of setting an image pick-up direction.
2. Description of the Related Art
When an automobile approaches an intersection, normally it will be necessary for a driver to ensure safety on left and right sides. At any intersection offering poor lateral visibility, however, the driver has had to cause the vehicle to enter the intersection zone a little bit so as to make sure of safety on left and right sides. Consequently, the driver needs paying careful attention to moving the vehicle into the intersection zone and also making sure of safety by directly watching scenes on both the left and right sides after entering the intersection zone, which has mentally given the driver a burden.
In order to reduce the aforementioned burden, there have recently been proposed a system of displaying images on the left and right sides of a vehicle, which images are picked up by image pick-up sensors such as CCDs fitted in the holes bored in the respective sides of an automotive bumper and displayed on a display unit such as a two-plane television installed in the vehicle; and a system of simultaneously displaying images on the left and right sides of a vehicle on a display unit provided in the vehicle by attaching a single image pick-up sensor onto the periphery of an automotive bumper or front glass and simultaneously taking in scenes on the left and right sides of the vehicle by means of the image pick-up sensor.
For example, JP-A-10-81173 discloses the former system, whereas JP-A-6-344827 discloses the latter system.
As shown in FIGS. 13 and 14, there has been proposed an apparatus for watching around a vehicle wherein images in the image pick-up directions 3L and 3R corresponding dead angles respectively on both left and right sides in the direction of travel A of a vehicle are picked up by an image pick-up apparatus 1 installed in the front end portion (front grille in this case) of the vehicle and utilized for driving. Such an image pick-up apparatus 1 may otherwise be installed in the rear end portion of a vehicle in order to pick up images in image pick-up directions corresponding dead angles in the direction of moving back a vehicle.
FIG. 15 is a block diagram showing the structure of a conventional apparatus for watching around a vehicle; and FIG. 16, a side view of the principal part of what is shown in FIG. 15. The apparatus for watching around a vehicle comprises a image pick-up apparatus 1, a processing portion 5, and a display unit 7 installed within a vehicle.
The image pick-up apparatus 1 has a light shielding case 11 provided with a pair of transmission windows 11L and 11R on both the respective sides thereof. In this case 11 exists an isosceles triangular prism (a reflective unit) 13 in cross section which is housed and placed in such a posture that its vertical angle side faces the front part of the case 11 (upper portion of the case 11 in FIG. 15) and that the lateral sides (first reflective surfaces) 13L and 13R of the prism corresponding to the isosceles of the isosceles triangle faces the respective transmission windows 11L and 11R. An image pick-up unit (an image pick-up unit) 15 is also housed so that it is positioned on the back side of the prism 13. The image pick-up unit 15 is equipped with an image pick-up element 15a and an image forming lens 15b disposed in the optical paths of rays of light 17L and 17R between the image pick-up element 15a and the prism 13.
Rays of light 17L and 17R incident from the image pick-up directions 3L and 3R on the lateral sides of the vehicle are incident onto the prism 13 via the both sides 13L and 13R of the prism, respectively. Then the rays of light 17L and 17R are wholly reflected from the respective sides 13L and 13R of the prism, and the optical paths are changed to directions substantially opposite to the direction of travel of the vehicle before being emitted from the prism 13 and incident on the image pick-up element 5a. Thus, images in the respective image pick-up directions 3L and 3R on both left and right sides are picked up by the single image pick-up element 15a. 
An image signal that is output from the image pick-up element 15a is input to the predetermined processing portion 5 and subjected to a predetermined process such as an inversion process. The processed image signal is supplied to the display unit 7, whereby the images in the image pick-up directions 3L and 3R are displayed by the image pick-up element 15a on the respective display areas 7L and 7R of the display unit 7.
The prism 13 in the conventional apparatus for watching around a vehicle is disposed in the case 11 so that both sides 13L and 13R of the prism may be laterally symmetrical with respect to the direction of travel A and in parallel to the vertical direction of the vehicle. Moreover, the image pick-up optical axis B of the image pick-up unit 15 is set parallel to the direction of travel A so that it may not lean to a horizontal plane C (see FIG. 17).
Accordingly, rays of light 17L′ and 17R′ on the incident optical axes out of the rays of light 17L and 17R that are reflected from the respective sides 13L and 13R of the prism 13 and incident from the image pick-up directions 3L and 3R are reflected at the reflective position P of the sides 13L and 13R of the prism and incident on the image pick-up unit 15 while the rays of light 17L′ and 17R′ are kept parallel to the horizontal plane C.
In the conventional apparatus for watching around a vehicle, images in the lateral image pick-up directions 3L and 3R are consequently picked up in such a state that the image pick-up optical axes defining the image pick-up directions 3L and 3R have been set parallel to the horizontal plane C.
FIG. 18 illustrates the state in which the picked up images are being displayed on the display unit 7 in the conventional apparatus for watching around a vehicle. In FIG. 18, reference numerals 21 and 23 refer to the bumper 9 of the vehicle; and 25 and 27 refer to images of the obstacles positioned on both left and right sides of the vehicle.
In the apparatus for watching around a vehicle like this, there is a case where the adjustment of the image pick-up directions 3L and 3R may be necessary by tilting them vertically with respect to the horizontal plane so as to obtain more useful peripheral images depending on the condition of installation of the image pick-up apparatus 1 including the position of installation of the image pick-up apparatus 1 on the vehicle, the configuration of the vehicle (configuration of the grille or the bumper 9 in particular) around the position of installation of the image pick-up apparatus and its periphery and so forth.
In the conventional apparatus for watching around a vehicle, however, the images 21 and 23 of the bumper 9 on the picked up image plane are too large in percentage and wasteful as shown in FIG. 18 under the influence of the conditions of installation of the image pick-up apparatus 1. Therefore, it is necessary to restrain the bumper 9 from being taken too much by correcting the image pick-up directions 3L and 3R upward.
As a method of changing the image pick-up directions 3L and 3R upward or downward in the conventional apparatus for watching around a vehicle, what is considered effective is to install the whole image pick-up apparatus 1 tilting in the vertical direction of the vehicle and to change the image pick-up directions 3L and 3R upward or downward by adjusting the angle of inclination.
However, there arises an inconvenience under the method stated above in that under an image of any pick-up object (e.g., building or telegraph pole) that actually uprightly exists is picked up and displayed as it is tilting with respect to the vertical direction.
This is due to the fact that when the image pick-up apparatus 1 is installed in the tilted condition, the sides 13L and 13R of the prism as the reflective surfaces of the prism 13 are also tilted with respect to the vertical direction, whereby the tilted image of the pick-up object is taken on the sides 13L and 13R of the prism when it is reflected from the sides 13L and 13R of the prism.
Although there is another method of changing the image pick-up directions 3L and 3R upward or downward with respect to the horizontal plane C by tiltably disposing the prism 13 in the vertical direction while the image pick-up optical axis B of the image pick-up unit 15 is held in parallel to the direction of travel A, the upright image is caused to tilt by the tilting of the sides 13L and 13R of the prism.
In addition, the following problems might occur in the conventional image pick-up apparatus.
1) Such an image pick-up sensor has been embedded in the bumper or fitted to the periphery of the front glass inside the vehicle, the heat radiation efficiency of the image pick-up sensor is poor and this has caused the performance of the image pick-up sensor to be lowered in high-temperature environment in summer. Consequently, it has been needed to improve the heat resistance of the image pick-up sensor, and a heat sink and the like used to cope with this situation have resulted in increasing the number of parts.
2) In case where rain drops, washing water drops and like stick to the outer surface of such a transmission window because of the rain falling, vehicle body washing and like, it is feared that the pick-up image may be disturbed by the refraction and scattering of rays of light caused thereby.